# What happens to the Magnetic field vector during polarisation of light?

According to a source http://electron6.phys.utk.edu/light/6/polarization.htm

It states that, "In general we pay more attention to the electric field E, because detectors such as the eye, photographic film, and CCDs interact with the electric field."

But we know a changing magnetic field produces an electric field and vice versa, so what exactly happens after light passes through a polaroid?

The electric field and the magnetic field of a propagating electromagnetic field are related by Maxwell's equations. This is true for all polarization states. So say you have a circularly polarized field that is propagating through a linear polarizer. Before the polarizer one can write down the electric field for the circularly polarized field and then use the appropriate Maxwell equation to calculate the associated magnetic field. The polarizer will remove one linear polarization component, leaving only the orthogonal linear polarization. Again one can then write down the electric field for the resulting linearly polarized field and then use the appropriate Maxwell equation to calculate the associated magnetic field.

• I am not sure that fully answers the question – Jyotishraj Thoudam Nov 19 '17 at 18:10

Light is periodic conversion of electric field to magnetic and back through Maxwell's equations.

You have to consider how polarizer works. Let's ignore the more complicated ways of polarizing light. Just think of it as wires in which current flows due to electric field, and this dissipates energy into heat. But why would this decrease the electric field AFTER the polarizer? Incoming electric field moves the electrons just electrons, which create an opposite field, so that the total field is nothing. But moving electrons also induce magnetic field, so you are cancelling this as well. In essence, you can think of the polarizer as a source that is cancelling the input source.

More roughly speaking: if you go electric-magnetic-electric-magnetic-.... and interrupt this sequence by destroying the electric field, there will be nothing to generate the next cycle of magnetic field.

Usually it is said that the electric field component of the photon interacts with the electric potential of the edges and a well designed to a range of light polarizer let throught approx. 50% of the light and reflect or absorb the other light.

But we know a changing magnetic field produces an electric field and vice versa, so what exactly happens after light passes through a polaroid?

is a very reasonable question in the case, one accept two axiomatic predictions

• the electric field of the surface electrons of an uncharged body is negleable
• the magnetic dipole moments of the surface electrons still exist and interaxts with the magnetic field component of the photon.

For the designer of a polarizer it's not important, what for approx. 50% of the photons is the reason, they get rotated and aligned during the approach to the polarizer. For an experimental physicist it is not easy to proof the axioms, they have to put an electric potential difference as well as a magnetic dipole moment between the slit's edges.

The axiomatic prediction follows from some fact, which are known but not enough interpreted.

1. First at all a neutral body can be charged with electrons and they stay on the body and not get throun away imediatly. This is strange because the last layer in a body are the surface electrons. So it coudl not be excluded that in an atom the electric charge is weakend (for both the electron and the proton).
2. Secondly if the electric field bewteen the electrons and the protons in an atom is weakend what hold the atom together? As you know the subatomic particles have the intrinsic property of magnetic dipole moment. It could not be excluded that this moments are responsible for the bound of the electrons to the nucleus (in detail see my paper About the distribution of electrons magnetic dipole moments in atoms)

So short answer, it could not be excluded that the magnetic field component of the photon is the real part of the EM radiation which interacts with the polarizer.